Kinetics of Peptides and Arginine Production from Microalgae (Scenedesmus sp.) by Flash Hydrolysis

Water under subcritical conditions in a continuous-flow reactor (flash hydrolysis) has proved to be an efficient and environmentally friendly method for hydrolyzing proteins from microalgae biomass in a very short residence time (few seconds). In this study, flash hydrolysis experiments were conducted at three different temperatures (240, 280, and 320 degrees C) and three residence times (6, 9, and 12 s) to understand the kinetics of the hydrolysis of algae proteins to water-soluble peptides and arginine. Laboratory-grown protein-rich Scenedesmus sp. with an average composition of 54% proteins, 17% lipids, and 23% carbohydrates was used as the feedstock. After flash hydrolysis, both liquid and solid products were collected, and the contents of soluble peptides and arginine in the liquid fraction and of remaining proteinaceous material in the solids were analyzed. For all experiments above 240 degrees C at all residence times, the yield of soluble peptides was in the range of 57-67% of the algae protein, whereas the maximum arginine yield (81.51%) was achieved at 320 degrees C and a residence time of 6 s. The protein solubilization to soluble peptides fitted second-order reaction kinetics, whereas for arginine, the process was zeroth-order; the activation energies were calculated to be 43.0 and 34.1 kJ/mol, respectively. The results of this study suggest that flash hydrolysis can be an environmentally benign method for hydrolyzing proteins from microalgae to produce valuable coproducts such as arginine as a free amino acid and water-soluble peptides along with lipid-rich solids (biofuel intermediate) as a feedstock for biofuel production.